DESCRIPTION (Adapted from Applicant's Description): Cartilage injury leading to osteoarthritis is a leading cause of disability in young people. Osteoarthritis, either based on cartilage injury or degeneration, is a leading cause of disability in the United States. Over the last several decades, much progress has been made in understanding cartilage injury and repair. MRI, with its unique ability to non-invasively image and characterize soft tissue, has shown promise in imaging cartilage. The goal of this proposal is to develop new MRI techniques to assess areas of cartilage damage and repair. Beyond simply demonstrating the morphology of an area of cartilage damage or repair, the investigators will use MRI to characterize the type of tissue present, which has implications about the prognosis and success of the repair. The proposal consists of three components. One is the development of the basic MR imaging technology. This will occur in parallel with the second component, i.e. studies of patients undergoing total knee replacement surgery. This will allow the assessment of the new imaging methods on the wide range of degenerative cartilage conditions typically present in such patients. Finally, a study will be performed to test these new methods in assessing and characterizing cartilage in patients who have had cartilage repair therapy three years previously. MRI holds much promise for assessment of cartilage injury and repair. Emerging therapies for cartilage injury require accurate, non-invasive assessment of repair tissue morphology and content. Development of new techniques to do this has the potential to allow rapid assessment of the effectiveness of these new therapies.